The present invention relates generally to automatic telephone answering apparatus and more particularly to a variable message recorder incorporating a grooveless disc for magnetically recording messages for playback and having a single motor to provide both turntable drive and spiral scanning of the disc and an optoelectronic system to initiate scanning at the same point on the disc for each successive record or playback operation.
Reference may be made to the following United States Pat. Nos: 3,500,363; 3,474,427; 3,250,856; 3,050,585; 2,975,238; and 2,680,150.
Automatic telephone answering apparatus is often used to monitor a subscriber's telephone for receipt of incoming calls in the subscriber's absence and to automatically transmit a pre-recorded message to the calling party in response thereto. Provision is also commonly made for recording a message from the caller for subsequent playback by the subscriber.
Prior art recorders employing phonographic-type apparatus using grooved discs or records for recording messages and tracking the associated transducer during playback have frequently been used in automatic telephone answering machines, dictating machines, and the like. One significant disadvantage of systems using a grooved disc, however, is that the grooved disc requires the use of a transducer having a very narrow poleface. Because of the extremely small surface area of the poleface bearing down on the groove of the disc, the per unit area loading pressure is very high, and accordingly, the life of the transducer is short.
Answering devices utilizing a grooveless disc and having a tone arm traversing the disc in a spiral fashion without following any mechanical groove to magnetically record and/or play back messages have been developed. These devices permit the use of a magnetic transducer having a much wider poleface to thereby reduce the per unit area loading. More particularly, these discs are generally similar in size and shape to the conventional grooved disc or record and are rotated on a conventional turntable. The tone arm is positioned adjacent the disc and rotated to permit radial scanning of the transducer across the disc. The magnetic transducer is disposed immediately adjacent the surface of the disc to either magnetically record a message on the disc or to play back a previously recorded message. Since the disc is grooveless, special processing of the disc is eliminated so that the disc can be cut from any recording stock having randomly oriented magnetic particles. However, elimination of the grooves precludes tracking of the tone arm across the disc by the usual mechanical interaction of the magnetic transducer riding in the spiral groove.
An alternative apparatus providing means for controlling the tone arm as it moves laterally across or scans a grooveless disc has previously been suggested in U.S. Pat. No. 3,047,663, issued July 31, 1962, to the inventor of the present invention and assigned to Electronic Secretary Industries, Inc. There, it was suggested to employ a spirally contoured cam driven by a first motor to move the follower arm of a tone arm assembly so that the tone arm automatically scans the disc as it rotates on a turntable driven by a second motor.
As the transducer scans or moves laterally across the rotating, grooveless disc, the message is recorded as a spiral magnetized line or path on the disc surface. Therefore, it is essential that the transducer be reset to the exact starting point of the message path for each successive playback. If the tone arm is not reset so that the magnetic transducer is at the starting point of the spiral path, the transducer will not follow the original path but rather will follow a different path. Of course, if the transducer does not follow the original spiral magnetized path, proper sound reproduction is not possible.
It was recognized in the aforementioned U.S. Pat. No. 3,047,663, however, that the positive or directly driven spiral cam, although normally providing satisfactory results does not take into account wear and slippage within the mechanism which may result in error in tracking the magnetized sound track.
Accordingly, an elaborate switching system including a synchronizing and latching switch was provided for automatically enabling the motor driven cam too radially scan the tone arm across the record in synchronism with the disc being rotated to a particular rotational position thereby insuring that the transducer follows the spiral track. The switch, mounted adjacent the turntable periphery, is periodically closed by physical contact with a small protrusion on the edge of the turntable thereby determining the starting point of the message track. Rotation of the turntable by the second motor is initiated through the complex switching system responsive to receipt of ringing current, i.e., whenever an incoming call is received. The synchronizing and latching switch combines with the remainder of the switching system to synchronize the initiation of tone arm scanning with the rotation of the turntable so that the transducer is set to the starting point of the message track to initiate scanning at the same point on the record every time.
There are, however, several disadvantages inherent in such a system. That is, two motors are required, as well as a complex switching system for properly synchronizing the operation of the motors to provide automatic tone arm scanning control. Moreover, the synchronizing and latching switch is subject to mechanical wear, substantially increasing the possibility that repairs will be needed. Finally, the switch must be carefully aligned with the turntable so that the synchonizing and latching switch is closed only when it contacts the protrusion, but not at any other time.